A selected ion flow tube (SIFT), study of the reactions of H3O+, NO+ and O2+ ions with a series of alkenes;: in support of SIFT-MS

We report the results of a detailed selected ion flow tube (SIFT) study at 300 K of the reactions of the 1-alkene and trans-2-alkene isomers of pentene, hexene, heptene, octene and nonene and I-decene (all liquids at room temperature) with H3O+, NO+ and O-2(+). All 33 reactions proceeded at the collisional rate under these SIFT conditions (helium carrier gas pressure of 0.7 Torr). The H3O+ reactions with both isomers of each alkene proceeded via exothermic proton transfer, which resulted in partial dissociation of the MH+ product ions for the longer chain alkene molecules, M, the number of fragment ions depending on the chain length. However, the mechanisms of the NO+ reactions were isomer specific, those involving the 1-alkenes proceeded via NO+ M production (three-body association) followed by partial stabilisation and partial dissociation of the nascent adduct ion to several products, including ions of the kind RHNO+ (R = CH3, C3H5, C4H7, etc,), whilst those involving the trans-2-alkene isomers proceeded partially via charge (electron) transfer to give M+ parent ions and via hydride ion (H-) transfer giving (M-H)(+) ions. The O-2(+) reactions all proceeded via charge transfer to give M+ ions together with multiple fragment ions. These O-2(+) SIFT data are compared and contrasted with the corresponding electron ionisation spectra (from the NIST database) for these alkenes. (C) 2002 Elsevier Science B.V. All rights reserved.